The present invention relates to a seat belt arrangement for a suspension seat installed in a vehicle, as well as a vehicle equipped with such a seat belt arrangement.
Some vehicles, in particular commercial vehicles, are equipped with suspension seats which accommodate the vehicle movements, therefore preventing health problems such us back pain for the seat occupant.
Like other types of seat, suspension seats are equipped with a seat belt arrangement including a seat belt which is designed to secure the seat occupant against harmful movement that may result during a collision or a sudden stop. A seat belt arrangement typically comprises a seat belt an end of which is mounted on a reel. The seat belt is attached on the seat by a first lower attachment point and by a lower deflection member removably locked in a second lower attachment point. An upper deflection point is further provided between the lower deflection member and the reel.
The structure, behaviour and use of a suspension seat being different from those of a fixed seat, specific and adapted features have been developed for the seat belt arrangements of suspension seats. However, the conventional seat belt arrangements for suspension seats are not fully satisfactory.
One first type of seat belt arrangement for a suspension seat provides for installing all components of the arrangement on the suspension seat, including the reel. This considerably increases the seat weight. This weight is further increased because the seat itself has to withstand the stresses in case of a sudden deceleration and therefore has to include the appropriate structural elements for that purpose. As a result, the seat cost is higher and its transportation is more complicated.
In order to save weight, one second type of seat belt arrangement for a suspension seat provides for installing part of the components of the arrangement on the vehicle frame, typically the reel and the upper deflection point. However, as the seat moves vertically with respect to the vehicle frame while the upper deflection point remains fixedly secured on the vehicle frame, the torso portion of the seat belt, between the upper deflection point and the lower deflection member, is not always adequately positioned relative to the seat, i.e. relative to the seat occupant. The latter may then experience discomfort, in particular due to continuous friction of the seat belt over his torso and cutting effect on his neck or face. The occupant's safety might even not been perfectly ensured in case the seat belt position is greatly offset from its appropriate position.
It therefore appears that from several standpoints, there is room for improvement in seat belt arrangements for suspension seats.
It is desirable to provide an improved seat belt arrangement for a suspension seat which can overcome the drawbacks of the prior art.
More particularly, it is desirable to provide a seat belt arrangement for a suspension seat installed in a vehicle which makes it possible to simplify the seat structure while ensuring the comfort and safety of the seat occupant.
According to a first aspect, the invention relates to a seat belt arrangement for a suspension seat installed in a vehicle, the suspension seat being capable of moving vertically relative to the vehicle frame in response to the vehicle movements, the seat belt arrangement comprising:                a seat belt having a first end portion intended to be secured to the seat at a first lower attachment point, and a second end portion mourned on a reel intended to be secured to the vehicle frame;        a lower deflection member slidably attached to the seat belt between said first end portion and said second end portion and equipped with a locking element intended to be removably locked in a second lower attachment point on the seat so that, when the lower deflection member is locked in said second lower attachment point, the direction of the seat belt is modified by the lower deflection member;        an upper deflection system to deviate the seat belt between the lower deflection member and the reel, and in or on which the seat belt may slide;        
a pivotable arm in or on which the upper deflection system is arranged and which is intended to be mounted on the vehicle frame so as to be able to automatically pivot about a pivot axis relative to the vehicle frame when the seat moves vertically, in order to keep the length of the torso portion of the seat belt, between the upper deflection system and the lower deflection member, substantially constant.
Thus, on the one hand, owing to the fact that the reel is intended, to be secured to the vehicle frame, the seat overall weight is decreased. Furthermore, as the upper deflection system is also attached to the vehicle frame, by means of the pivotable arm, the invention makes it possible to relieve strain from the seat, since the strains due to a strong deceleration or even a collision can be taken up by the vehicle frame. This further allows a decreasing of the seat weight.
On the other hand, positioning these components of the seat belt arrangement on the vehicle frame is not done to the detriment of comfort nor safety. Indeed, because the length of the torso portion of the seat belt is kept substantially constant and the variations of the seat belt tension are reduced by means of the pivotable arm, the seat belt is continuously properly maintained over the seat occupant's torso, despite the fact that the seat moves vertically while the upper deflection system is mounted on the vehicle frame.
In practice, the length of the torso portion of the seat belt remains substantially unchanged. Of course, a slight length variation, for example not exceeding 5%, may occur the torso portion, provided this variation does not substantially impair the occupant's comfort and safety.
In other words, the invention makes it possible to keep the height of the upper deflection system relative to the seat substantially constant. It has to be noted that this correspond to a continuous adjustment, i.e. an adjustment in permanent mode, and not an initial adjustment that the seat occupant makes once for putting, the upper deflection system at the appropriate height according to his morphology.
In practice, the pivotable arm includes a body and the upper deflection system which is attached to the body. The upper deflection system can either be fixedly attached to the body or include at least one part movable with respect to the body. The pivotable arm can be substantially rigid and non deformable, and capable of pivoting about the pivot axis. Alternatively, at least part of the pivotable arm body can be made of a semi rigid material capable of undergoing an elastic deformation corresponding to a pivoting movement of the upper deflection system relative to the pivot axis.
The seat belt arrangement may also comprise elastic return means arranged to urge the pivotable arm towards a predetermined neutral position, the return force of said elastic return means being set to compensate the pulling force exerted on the pivotable arm when the seat moves vertically, in order to keep the length of the torso portion of the seat belt and the seat belt tension substantially constant.
In an advantageous embodiment, the upper deflection system is arranged on a front end of the pivotable arm, the pivot axis being offset rearward from the upper deflection system, in the mounted position, i.e. when the seat belt arrangement is mounted on a seat in the vehicle. Thus, the pivoting of the pivotable arm results in the upper deflection system being lowered or raised relative to the seat.
The term “front end of the pivotable arm” refers to an end of the pivotable arm that extends towards the front of the vehicle when the seat belt arrangement is mounted with a suspension seat in the vehicle.
The term “offset rearward” refers to a direction that extends from the front to the rear of the vehicle when the seat belt arrangement is mounted with a suspension seat in the vehicle.
Moreover, this disposition makes the seat belt easier to grab as compared to conventional suspension seats having a seat belt which in nominal position lies flat on the backrest. Indeed, owing to the invention, the upper deflection system can be located forward with respect to the seat backrest.
In a preferred embodiment, the pivotable arm comprises braking means capable of restraining or blocking the movement of the seat belt relative to the upper deflection system when the seat moves vertically. These braking means may be arranged on various parts of the pivotable arm, typically on a body of the pivotable arm or on the upper deflection system which is mounted on said body of the pivotable arm. Advantageously, these are self braking means, i.e. means that are activated automatically and without the implementation of another component, when there is a need to limit the movement of the seat belt relative to the upper deflection system.
The braking means may comprise friction means designed to cooperate with the seat belt so as to substantially prevent the seat belt from sliding relative to said upper deflection system in normal operation and when the seat is moving vertically, and to allow the seat belt to slide relative to said upper deflection system following a manual traction by a user. Preferably the friction means are designed such that the friction force generated between the friction means and the seat belt is greater than the seat belt tensile force that causes the rotation of the pivotable arm about said pivot axis.
In other words, in this implementation, the seat belt arrangement makes it possible to keep the length of the torso portion of the seat belt substantially constant and to reduce the variations in the seat belt tension through friction means which are arranged on the upper deflection system, and which are the means allowing the seat belt to make the arm pivot in normal operation. These features also prevent the seat belt from being too loose or too tight on the seat occupant's torso.
The braking means are constituted by or include the friction means, and are preferably arranged on the upper deflection system.
With this implementation, there is no need for a mechanical link between the seat and the upper deflection system—for example between the seat and the pivoting arm—in order to cause an automatic movement of the pivotable arm in response to a seat movement. The seat belt arrangement is therefore less complicated and more robust. However, providing such a mechanical link would be a possible alternative technical solution.
“In normal operation” means in steady state, i.e. when an occupant is sat on said suspension seat and has fastened his seat belt. Then, in order for the seat belt arrangement to work adequately, the friction means prevent the belt from sliding relative to the upper deflection system both when the suspension seat moves downward and upward. The manual traction exerted by a user corresponds to a transient state, when the user, i.e. the seat occupant, pulls the seat belt in order to put it on. During this transient state, the sliding of the belt relative to the upper deflection system can be allowed for example because the force exerted on said seat belt is higher and/or because the orientation of the seat belt is different from its orientation in normal operation, resulting in a lower level of friction on the upper deflection system.
For example, the friction means can comprise an anti slip surface, including an anti slip material and/or relief patterns.
In an embodiment, the braking means can comprise at least one movable member which can move with respect to a body of the pivotable arm between a blocking position, in which the seat belt cannot slide relative to said upper deflection system in normal operation, and a release position, in which the seat belt can slide relative to said upper deflection system. Preferably, the movable member can be in the release position only when a user pulls on the seat belt. In said release position, the friction level is lower, typically because the contact area is smaller. This can be achieved for example because the seat belt has been partly moved away from a contact area, or because the shape of the contact area has been changed.
The seat belt arrangement may comprise a spring member designed to stress said movable member towards its release position, the movable member being able to be moved towards the blocking position, against the spring force, by the seat belt in normal operation.
Alternatively, the seat belt arrangement may comprise a spring member designed to stress said movable member towards its blocking position, the movable member being able to be moved towards the release position, against the spring force, through a manual action of a user pulling on the seat belt.
In another embodiment, the upper deflection system can be fixed with respect to a body of the pivotable arm and can comprise a bearing surface for the seat belt which is at least partially substantially cylindrical in shape, said friction means being arranged on said bearing surface.
The whole bearing surface can then be covered with an anti slip surface.
It may be envisaged that the bearing surface includes a retractable flap which is maintained substantially level with the remaining portion of the bearing surface in normal operation and which protrudes outward when a user pulls on the seat belt. An anti slip surface may cover at least part of the retractable flap and/or at least part of the remaining portion of the bearing surface.
In an implementation of the invention, the upper deflection system can comprise a plurality of rolls capable of forming a winding path for the seat belt, thereby braking the movement of the seat belt relative the upper deflection system.
For example, at least one roll is movable relative to the other roll(s) between a first position in which the path is designed to generate a first level of friction, which is sufficient to cause braking, and a second position, in which said roll is located farther from the other roll(s), so that the path is less winding and generates a second level of friction which is lower than the first one.
It may be envisaged that the upper deflection system comprises at least one roll rotatably mounted on a body of the pivotable arm and having friction means arranged on its outer surface, the braking means being arranged to hinder the free rotation of said roll with respect to the pivotable arm body.
Besides, the pivotable arm is preferably designed to be collapsible towards a security configuration, in which its front end has moved rearward and/or upward, in case the vehicle is subjected to a shock or to an deceleration exceeding a predetermined level. This can typically happen in case the vehicle suddenly brakes or stops, for example during a collision.
Owing to this feature, the pivotable arm does not affect safety in case of an accident, since there is no risk for the seat occupant to hit the pivotable arm insofar has it has moved away from the occupant. Another advantage of this disposition is that it further entails a pretension of the seat belt, ensuring the seat occupant is maintained against the backrest.
In practice, the pivotable arm can be made of a material capable of being elastically deformed towards a security configuration in case of a collision. Alternatively, the pivotable arm can be substantially rigid, means being then provided to move it towards the security configuration.
The seat belt arrangement can comprise a safety actuator coupled to a sensor capable of detecting a strong deceleration of the vehicle or capable of detecting a shock on the vehicle, for example due to a collision with another vehicle or with a static obstacle, the safety actuator being capable of quickly pivoting the pivotable arm. The term “quickly” means that the pivoting movement is provoked sufficiently fast to avoid the seat occupant, who also undergoes an unintentional displacement due to the strong deceleration, hitting said pivotable arm.
The sensor can comprise a shock detector or an accelerometer, while the safety actuator can comprise an electromagnetic device or a pyrotechnic device for example.
In an embodiment, the safety actuator can include:                elastic, return means capable of urging the pivotable arm towards the neutral position;        a retaining element which cooperates with the elastic return means in normal operation in order to prevent them from stressing the pivotable arm beyond the neutral position;        a deactivating element capable of deactivating the retaining element so that the elastic return means can move the pivotable arm beyond the neutral position towards the security configuration.        
In another embodiment, the safety actuator can be distinct from said elastic return means, said safety actuator, that can be an electromagnetic device or a pyrotechnic device, being designed not to hinder the normal operation of the elastic return means and, following a shock or an deceleration exceeding a predetermined level, to cause the pivotable arm to pivot despite or in addition to the elastic return means. Depending on the configuration of the seat belt arrangement, the safety actuator can be designed to overcome the force of said elastic return means or, on the contrary, to supplement said force.
According to a second aspect, the invention relates to a vehicle comprising:                a frame;        a suspension seat installed so as to be capable of moving vertically relative to the vehicle frame in response to the vehicle movements, the suspension seat including a first and a second lower attachment points;        and a seat belt arrangement as previously described, the seat belt first end portion being secured to the seat at the first lower attachment point, the reel on which the seat belt second end is mounted being secured to the vehicle frame, and the pivotable arm being pivotably mounted on the vehicle frame about a pivot axis.        
For example, the pivot axis is substantially transversal to the vehicle and offset rearward from the upper deflection system.
Advantageously, the upper deflection system can be located forward from the seat backrest. By providing a gap between the seat backrest and the seat belt, the invention allows the seat belt to be easier to grab. Since the user does not need to catch the seat belt behind his shoulder and does not experience difficulties in grabbing it, he is more likely to use it, even if he has to make this gesture several times a day, like distribution drivers.
Furthermore, in an implementation, the pivot axis position on the vehicle can be adjusted longitudinally and/or vertically. This makes it possible to adapt the seat belt arrangement to the seat occupant's morphology. It has to be noted that this adjustment has to be made one and for all by a specific user, and has nothing to do with the continuous and automatic movement of the pivotable arm following the vertical movements of the seat during normal operation.
Typically, the pivot axis can be arranged on the vehicle B-pillar. These and other features and advantages will become apparent upon reading the following description in view of the drawing attached hereto representing, as non-limiting examples, embodiments of a vehicle according to the invention.